1. Field of the Invention
This invention relates to an optically active pyranobenzoxadiazole compound, which is an important intermediate in the synthesis of an optically active pyranobenzoxadiazole derivative useful for the treatment of hypertension and asthma, and a process for the optical resolution of a pyranobenzoxadiazole compound.
2. Description of the Prior Art
A pyranobenzoxadiazole derivative represented by the formula [III] (which will be briefly referred to as the compound [III] hereinafter): ##STR3## wherein A represents a hydroxyl group or an OC(O)CH.sub.3-n X.sub.n group in which X represents a fluorine atom, a chlorine atom, a bromine atom, a methyl group or a methoxy group and n represents 0 or an integer of 1 to 3;
when R.sup.1 represents a hydrogen atom, R.sup.2 represents a hydrogen atom, C(Z)CH.sub.3-n X.sub.n group, in which Z represents an oxygen atom or a sulfur atom and X and n is as defined above, or C(Z)NHCH.sub.3-n X.sub.n group, in which Z and n are defined above; and
when R.sup.1 does not represent a hydrogen atom, R.sup.1 and R.sup.2 together represent (CH.sub.2).sub.m-1 C(Z) group, in which m represent an integer of 4 or 5 and Z is as defined above, (CH.sub.2).sub.m-2 NHC(Z) group or a (CH.sub.2).sub.m-2 OC(Z) group, in which Z and m are as defined above,
is obtained in the form of a racemic mixture as described in Japanese Patent Laid-open No. Hei 2-49788 (49788/1990) and U.S. Pat. No. 4,900,752. The compound [III] exerts intense vasodilatory and hypotensive activities and thus is expected to be useful as a medicine for treating hypertension, angina pectoris, arrhythmia, cerebral circulation disorders and asthma.
As described in the Japanese Patent Laid-Open No. Hei 2-49788 (49788/1990), the compound [III] can be synthesized in the following manner: